Two populations of rats (Rattus norvegicus) were studied for 18 months in complex, compartmentalized habitats to determine if acquisition of cooperative behavior could prevent the origin of behavioral pathologies which usually accompany crowding level densities. Members of the experimental population were required to learn two quite different and complex types of cooperative behavior, one to obtain water and the other to obtain food. Learning and maintaining these cooperative behaviors takes considerable time. Preliminary analyses indicate that the two sexes gain this time in quite different ways. Females in the two populations became pregnant in equal frequency. However, experimentals reared only 40% of their litters; the remainder disappeared very shortly after birth. This manner of "avoiding" rearing young provided time for the experimental females to learn and maintain cooperative behavior. Experimental males apparently gain the necessary time for learning cooperative behavior by reducing the frequency and duration of status interactions. Strategies have been developed for obtaining precise measures of how much reproductive and status behavior time is utilized by experimentals in order to develop cooperative behavior. These measures are deduced from movements each rat makes between compartments of the habitat. Special technology records ca. 200 passages per rat, by its I.D., each day over its life span, for each of 80 rats. These passages between compartments, in conjunction with extensive observations of status interactions, permit calculation of an index, termed "social velocity", which reflects behavioral competence, and degrees of participation in opportunities for behaving. This index should prove to be particularly useful in our analysis of how the experimental cooperative population moves in the direction of decreased entropy, that is to say, toward increased diversity, complexity, organization, adaptability and capacity to process information. These latter anti-entropy processes comprise increase in negentropy.